YAKIMA, Wash. — Five or six years ago, the Tieton bighorn herd included nearly 200 sheep. Now it has fewer than 10 — the same ones drivers occasionally see licking U.S. Highway 12 rumble strips for what's left of last winter's salt-based de-icer.

Soon enough, those few remaining bighorns will be gone. Either they'll die on their own or they'll be shot by agents of the same state wildlife department that put them there in the first place.

A pneumonia outbreak, presumed to have been transmitted from domestic sheep or goats that carry the disease-causing pathogens but are largely immune to them, wiped out about 100 members of the herd between last fall and this spring.

Since last month, Washington Department of Fish and Wildlife officials have killed another 49 of the herd to keep the disease from spreading to the neighboring, still disease-free Cleman Mountain herd.

In the next year or two, those officials expect to begin the process of restarting the herd with transplanted animals from healthy herds — the same way they did it the first time in 1997, when they brought in bighorns from Oregon, Canada and elsewhere in Washington.

The Tieton herd “went from no sheep to a small huntable population within five or six years, so hopefully we can do that again,” said Ted Clausing, the state's regional wildlife program director. “It's still a valuable resource, and having another herd is a good thing. (Another die-off) could happen in the Cleman next time, and it would be nice to have a healthy herd right next door.

“If you only have a few (herds) around the state, you're at much greater risk (of a catastrophic die-off) than if you have a lot of them, in which each one can sustain itself.”

The 1997 reintroduction of bighorns into the Tieton area generated opposition from some Forest Service officials.

It came on the heels of the 1995-'96 Hell's Canyon bighorn die-off, caused by pathogens believed to have been transmitted to the bighorns by a feral goat — and numerous Tieton or Naches-area homeowners own sheep or goats. Also, the Moxee-based Martinez sheep operation had three active grazing allotments, all of them decades old, in the Rattlesnake, Nile and Naches areas of the Wenatchee National Forest, where the Tieton bighorns might wander.

Nick Martinez said even if his family business loses grazing allotments over the Tieton die-off, wildlife officials will still have a hard time protecting bighorns against infection.

“Are they totally going to eliminate all the risk to the bighorns?” he said. “Even if they kick us out, we're probably a lesser risk than some others they've got. There's a lot of sheep and goats closer (to the bighorns) than we are, but they're on private land and (public officials) can't do anything to them.”

Ironically, the Martinez grazing allotments have been much closer to the Cleman herd — which remains disease-free largely because their efforts to ensure no contact between the domestic sheep and the bighorns.

“We run (the Martinez operatives) pretty hard, and they've done everything we've ever asked of them,” said Carla Jaeger,a range technician for the Wenatchee National Forest.

When cougars or other predators go after grazing sheep, though, the ewes and lambs can scatter and become hard for herders to keep track of. And that may well be what happened last year.

At the end of the 2012 grazing season, herders bringing out the Martinezes' Nile-area allotment discovered that as many as 20 sheep were missing. All but a couple lambs were eventually found, but one lamb actually survived the winter and was found in March — and killed, by a Martinez employee — on the south side of the Naches River.

The animal's carcass was tested at Washington State University and found to be carrying the same pathogen found in each of the tested carcasses of the Tieton bighorns. But while that makes it likely the bighorns were infected by the grazing sheep, it's not a certainty.

“Even if it (turns out to be) an identical strain, we can't tell which way the transmission went,” said WSU's Thomas Besser, an expert in veterinary pathology who did the testing.

“Did it go from the domestic to the bighorn or was it transmitted the other way? We don't know.”

Besser, though, has tested numerous Tieton bighorns over the past three or four years for evidence of Mycoplasma ovipneumoniae, a pathogen that has been present in all 37 of the bighorn pneumonia outbreaks he has studied, and never found any. Until now.